gfs2: separate holder for rgrps in gfs2_rename

Before this patch, gfs2_rename added a holder for the rgrp glock to
its array of holders, ghs. There's nothing wrong with that, but this
patch separates it into a separate holder. This is done to ensure
it's always locked last as per the proper glock lock ordering,
and also to pave the way for a future patch in which we will
lock the non-rgrp glocks asynchronously.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/inode.c

@@ -1348,7 +1348,7 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
 	struct gfs2_inode *ip = GFS2_I(d_inode(odentry));
 	struct gfs2_inode *nip = NULL;
 	struct gfs2_sbd *sdp = GFS2_SB(odir);
-	struct gfs2_holder ghs[5], r_gh;
+	struct gfs2_holder ghs[4], r_gh, rd_gh;
 	struct gfs2_rgrpd *nrgd;
 	unsigned int num_gh;
 	int dir_rename = 0;
@@ -1357,6 +1357,7 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
 	int error;
 
 	gfs2_holder_mark_uninitialized(&r_gh);
+	gfs2_holder_mark_uninitialized(&rd_gh);
 	if (d_really_is_positive(ndentry)) {
 		nip = GFS2_I(d_inode(ndentry));
 		if (ip == nip)
@@ -1398,13 +1399,6 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
 	if (nip) {
 		gfs2_holder_init(nip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
 		num_gh++;
-		/* grab the resource lock for unlink flag twiddling 
-		 * this is the case of the target file already existing
-		 * so we unlink before doing the rename
-		 */
-		nrgd = gfs2_blk2rgrpd(sdp, nip->i_no_addr, 1);
-		if (nrgd)
-			gfs2_holder_init(nrgd->rd_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh++);
 	}
 
 	for (x = 0; x < num_gh; x++) {
@@ -1413,6 +1407,22 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
 			goto out_gunlock;
 	}
 
+	if (nip) {
+		/* Grab the resource group glock for unlink flag twiddling.
+		 * This is the case where the target dinode already exists
+		 * so we unlink before doing the rename.
+		 */
+		nrgd = gfs2_blk2rgrpd(sdp, nip->i_no_addr, 1);
+		if (!nrgd) {
+			error = -ENOENT;
+			goto out_gunlock;
+		}
+		error = gfs2_glock_nq_init(nrgd->rd_gl, LM_ST_EXCLUSIVE, 0,
+					   &rd_gh);
+		if (error)
+			goto out_gunlock;
+	}
+
 	error = -ENOENT;
 	if (ip->i_inode.i_nlink == 0)
 		goto out_gunlock;
@@ -1541,6 +1551,9 @@ static int gfs2_rename(struct inode *odir, struct dentry *odentry,
 		gfs2_quota_unlock(ndip);
 out_gunlock:
 	gfs2_dir_no_add(&da);
+	if (gfs2_holder_initialized(&rd_gh))
+		gfs2_glock_dq_uninit(&rd_gh);
+
 	while (x--) {
 		gfs2_glock_dq(ghs + x);
 		gfs2_holder_uninit(ghs + x);